Santa Cruz County among most susceptible to landslides statewide

SANTA CRUZ - Here's one that comes as no surprise to the residents of Nelson Road - Santa Cruz County is among the highest-risk counties for landslides in Northern California, according to the California Geological Survey.

With a handful of Scotts Valley residents still working around a massive rockslide caused by torrential March rains, the California Geological Survey on Thursday released a map showing the dangers of landslides around the state. The Santa Cruz Mountains join parts of Marin County and the East Bay where residents should be on alert that steep slopes and rock instability could cause the ground to slide out from under them.

"Santa Cruz stands out even within the Bay Area because it has higher mountains, steeper slopes, and it has weaker rocks," said Chris Wills, a state supervising engineering geologist.

The maps look strictly at geological risks, without taking into account fire storms, earthquakes or weather patterns that could trigger landslides. When those are included, the county - which is used to all three - could move up on the list as potential disaster sites. Wills said the next step is to take weather into account.

"The goal in this was to develop a scenario for a major winter storm that we could talk to emergency managers about," he said.

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About 57,000 landslides were mapped as part of the project, which was done in support of the U.S. Geological Survey's ARkStorm Scenario, which envisions a storm that brings up to 10 feet of rain and causes $300 billion in damage statewide. The recent March storms caused an estimated $44 million in damage statewide.

But despite widespread anecdotal evidence that could stake the county as California's landslide capital - 1983's Love Creek disaster that claimed 10 lives is part of county lore - the biggest risks for slides appear to be in Southern California, including Santa Barbara and Ventura counties.

"There are very weak rocks in pretty much all parts of the state," Wills said.

The county's risk areas include the coastal ranges north of Santa Cruz and relatively more populated mountain areas between Highway 9 and across to the city of Watsonville. The most-dangerous area for landslides appears to coincide with an unpopulated region of the county, the Forest of Nisene Marks State Park.

Southern parts of Monterey County on either side of the tip of the Salinas Valley are also slide-prone.

Paul Horvat, the county's emergency services manager, said the county already analyzes landscape risks, especially in regions affected by a fire. The county even sends notices to residents warning them of the danger and holds community meetings to go over the findings.

And emergency managers still rely on an old standby when it comes to understanding local landslide risks - experience.

"A lot of my knowledge is based on past events and experience in the area," Horvat said.

To calculate the risks, the California Geological Survey used two factors: slope steepness and rock stability. Areas with previous rockslides were candidates for more slides, since the ground is already weakened.